In a scanning electron microscope (SEM), a focused electron beam is scanned across the surface of a specimen. Signals (typically electrons) emitted from the region of the surface struck by the incident electron beam are detected, typically by a solid state diode or by a scintillator or phosphor that is optically coupled to a photomultiplier, and the current generated by the detected signal determines the current of a beam of electrons in a cathode ray tube (CRT). As the focused electron beam is scanned over the surface, an image is built up on the CRT. SEM's are well known in the art and well described, for example, in numerous publications, among the first of which is by D. McMullan entitled “An improved scanning electron microscope for opaque specimens.” published in Proc. IEE vol. 100 Part II, 245-259 (1953).
A particular type of SEM is one in which the specimen is placed in the high field region of the magnetic lens of the microscope. Such microscopes are called immersion lens SEM's, and can produce better resolution for the same beam energy.
In particular, the magnetic field at the focus of an SEM can be used to energy analyze the backscattered electrons from a specimen, as explained in great detail by U.S. Pat. No. 4,962,306 issued Oct. 9, 1990.
U.S. Pat. Nos. 7,105,817, 6,768,111, and 5,408,098 give further details of the use of SEM's in imaging and in topographical measurement. All of the above applications are hereby incorporated herein by reference in their entirety including incorporated material.